Toddlers wake up from there sleep crying and screaming suddenly. It is nothing abnormal. There is nothing to worry about. Toddlers dream like we do. We are a little more conscious about what we see being just a dream, but toddlers usually cry because of bad dreams or of feelings that they had when they were still in the mother's womb. It is not harmful as toddlers do not remember their dreams and will forget all about a bad dream the next morning. Most toddlers who sleep when they are exhausted or have not eaten enough get cramps or leg aches or sudden hunger pans, the pain could be another reason they cry.